O O Emenalom, A B I Udedibie, B O Esonu, E B Etuk and H I Emenike

Abstract

Velvet bean (Mucuna pruriens) is a tropical legume, which
has potential as an energy and protein supplement in livestock feeds.
Unfortunately, the use of raw velvet bean in non-ruminant feeding
is limited because of its content of anti-nutritional
factors.

A 42-day feeding trial was conducted to determine the response
of growing pigs to diets containing unprocessed, or processed (cracked, soaked
and cooked) velvet beans. Unprocessed velvet bean seeds were dried
and milled and incorporated at 15% dietary level, while another
batch was cracked, soaked in water for 48 hours and cooked for 60
minutes, dried, ground and incorporated at 20%, 30% and 40%
dietary levels. The control (0%) diet contained no velvet bean. Each diet
was fed to four growing pigs. At the end of
the 42nd day, two pigs per treatment were fattened for 7
days, fasted for 18 hours, slaughtered and eviscerated for organ
weight determination. Unprocessed velvet bean at 15% dietary level
significantly depressed the general performance of
the pigs when compared with other groups. The groups on cracked,
soaked and cooked velvet bean diets performed significantly better in growth
rate and feed conversion than the group on
unprocessed velvet bean and compared favourably with the group on
the control diet. Unprocesed velvet bean significantly decreased the organ weights of the pigs. Mortalities
recorded among the group on velvet bean were attributed to the
treatments.

It is suggested that 15% dietary level of unprocessed velvet
bean is toxic to pigs and that cracking prior to soaking in water and cooking
allows for a successful use of the bean, up to 40% in the diets of growing pigs.

Key words: Pigs, processing, toxicity, velvet bean

Introduction

Many indigenous tropical legumes can be said to be "under utilized" because little has been done to explore ways to stimulate their production, processing, marketing or use. However, with the
ever increasing demand for energy and protein feedstuffs and the
subsequent competition between humans and livestock for the few
available grains, there is need to explore ways to exploit these
indigenous legumes, one of which is velvet bean (Mucuna
pruriens) which is widely used as a cover crop (Berhe
2001).

Velvet bean is high in protein (Emenalom and Udedibie 1998) but
contains toxic substances (Siddhuraju Vijayakumari and
Janardhanan1996) that can be destroyed by heating (Udedibie and
Carlini 1998). Few data are available on the use of velvet bean in pig
nutrition. David (1986) reported that the raw seeds are not
utilized by poultry but can comprise up to 25% of a ration for
pigs. EDN (1997), in contrast, observed that while the seeds
usually give good results with cattle and sheep even when fed up to
70% of the diet, they are generally unsatisfactory for pigs when forming up to
5% of the ration and may even cause severe vomiting and diarrhoea
at 25% dietary level. Studies with poultry have shown that the raw
bean is toxic to broilers (Emenalom and Udedibie 1998; Carmen et
al 1999; Esonu 2001) and that cooking the bean (Emenalom and
Udedibie 1998) only gave indications of partial detoxification
hence its dietary inclusions could not exceed 10%. Soaking the bean
in water before cooking (Udedibie et al 2001) allowed for a
successful use of the bean at 20% for broilers.

Recently, Emenalom et al (2002) observed that cracking
the bean into 2 to 4 pieces before soaking in water and cooking was
more effective in improving the performance of broilers. This
procedure has not been used for pig rations. This study was
therefore designed to evaluate the response of pigs to diets
containing raw, and crack - soak - and - cook velvet
bean.

Materials and methods

The velvet beans used were divided into two batches.
The first batch of the seeds (VB) was air-dried, ground and
incorporated into the diets of grower pigs at 0% (control) and 15%
levels. The second batch was cracked into 2 to 4 pieces
using an ASKO AII (manufactured by Nigerian electrical plants ltd)
grinding machine. The cracked beans were soaked in water for 48
hours (after which the water was discarded), rinsed with fresh water,
cooked for an hour (period of cooking was taken as starting from
the point of boiling), sun dried and milled to produce cracked, soaked and
cooked meal (PVB). This meal was incorporated in
the diets of grower pigs at 20, 30 and 40% levels respectively
(Table 1).

Twenty crossbred pigs (Large White x Land race) of
mixed sexes having body weights of 17.0 to17.5 kg were
divided into five groups of four pigs each and randomly assigned to
the five experimental diets in a completely randomised design. Each treatment was replicated four times
with the pigs housed
individually, weighed at the beginning of the experiment and weekly
thereafter. Rations were offered at four percent of body weight
adjusted weekly, while water was provided ad libitum. At the
end of the 42-day feeding period, 2 pigs from each group were
fattened for another 7 days on their different diets, fasted for 18
hours, weighed, slaughtered and eviscerated. Weights of the liver,
heart, kidney, lungs and carcass yield were recorded and expressed
as percentage of live weights.

The data collected were subjected to analysis of variance
(Snedecor and Cochran 1967). Where the analysis of variance indicated
significant treatment effects, the means were compared using Duncan's
New Multiple Range Test (DNMRT) as outlined by Obi
(1990).

Results and discussion

The data on the performance and organ characteristics
of the experimental pigs are shown in Tables 2 and 3.

abc: means
within a row without superscript in common differ at P < 0.05

The deleterious effects of raw velvet bean on weekly weight gains are shown
in Figure1. After 42 days feeding, pigs fed 15% velvet bean
gained 56.8% of control as against 94.8% gained by pigs fed a
ration containing 40% processed velvet bean. Pigs on 15% velvet bean diet
recorded a slight decline in feed intake but a significantly poorer feed conversion ratio.
The weights of heart, kidney and lungs were lowest for the15%
dietary inclusion of unprocessed velvet bean. Fifty percent
mortality was recorded in the 15% velvet bean group.

Figure 1: Effect of velvet bean meals on the growth of
young pigs
(PVB is processed velvet beans and RVB is unprocessed beans)

The result was consistent with the findings of Khan et al
(1979) who showed that heat treatment applied to legume foods
improves their texture, palatability and nutritive value by
destroying or inactivating heat-labile toxic compounds and other
enzyme inhibitors. The increase in weekly weight gains in pigs fed
20, 30 and 40% velvet bean rations is particularly notable in view
of the treatment applied to the seed. Josephine and Janardhanan
(1992) and Ravindran and Ravindran (1998) reported that except for
L. Dopa all anti-nutritional factors detected/quantified in
Mucuna beans are heat-labile and could be eliminated by
cooking. However, the denaturation of heat-labile inhibitors by
thermal processing (Liener and Kakade 1969) is governed by
temperature, duration of heating, particle size and moisture
contents. Thus cracking the seeds prior to soaking and cooking
reduced the particle size and increased the moisture contents of
the seeds, and facilitated the cooking to softness at one hour
contrary to 2.5 hours reported for whole soaked-seeds (Wanjekeche
2001). It appears that the practice of cracking prior to soaking
and cooking improved the nutritive value of the bean for pigs.
However, presence of L-Dopa and other anti-nutritional factors in
Mucuna bean might have contributed to the decreased growth
of pigs fed 15% velvet bean ration as against the processed velvet bean
groups. This is in agreement with the reports of EDN (1997) that
raw Mucuna bean is poisonous to pigs at any dietary level,
but contradicted the findings of David (1986) that Mucuna
bean would be tolerated by pigs up to 25% in the
ration.

The slightly reduced feed intake of pigs fed 15% raw velvet bean
could be attributed to the variations in the weekly weights of the
pigs since they were fed 4% of their body weights adjusted weekly.
It appeared therefore that inclusion of raw velvet bean at 15% and
processed velvet bean at 20, 30 and 40% respectively did not affect
feed intake of the pigs unlike raw or processed jackbean (Canavalia
ensiformis) which was rejected by pigs when
incorporated either raw or cooked in the rations (Emenike 1998) . The poor feed
conversion ratio recorded in the 15% group was attributed to
anti-nutritional factors present in the bean, which may have
affected nutrient utilization and absorption. Generally pigs on processed velvet bean rations had good feed conversion ratios comparable
to the control group.

The factors responsible for the high mortality and depressed organ weights of
pigs fed 15% raw velvet bean were not clear and
need further investigation. There were also observable changes in the colour of
the lungs (from brick red to pale yellow) and accumulation of fluid in the
bladder of the pigs fed 15% velvet bean rations. These observations showed that
unprocessed seeds of velvet bean are not safe for use in pig rations (even at an
inclusion level of 15%) but cracking the bean prior to soaking in
water and cooking could allow for up to 40% inclusion in the
rations of young grower pigs.

Acknowledgement

The authors are grateful to the International Foundation for
Science (IFS), Sweden for financing the research.